The present invention relates generally to a process for electrodepositing metal, and more particularly, to an electroforming cell for forming metal foil, the cell having means for applying a surface treatment to the metal foil. The present invention is particularly applicable in forming thin copper foil and will be described with particular reference thereto; it being understood, however, that the present invention may also find advantageous application in electroforming and surface treating other metal foils.
The basic technique in forming electrodeposited foil has not changed greatly over the years. In this respect, electrodeposited copper foil is generally formed by immersing a rotating drum cathode in an electrolyte solution containing copper ions. An anode formed from one or more arcuate sections of electrically conductive material is immersed in the electrolyte solution and positioned adjacent the drum cathode. The anode is formed to have a surface generally conforming to the curvature of the drum cathode so as to define a uniform inner electrode gap therebetween. Copper foil is formed on the rotating drum by applying a current, having a current density lower than the limiting current density of the electrolyte solution, to the anode and cathode. The electrodeposited foil is continually removed from the drum cathode as it emerges from the electrolyte solution so as to permit continuous foil production.
Typically, the electrodeposited copper foil formed in accordance with the foregoing process is then surface treated to improve and enhance the surface of the foil for bonding the same to another surface, typically a polymeric substrate. This latter surface treatment process, sometimes called a xe2x80x9cbonding treatmentxe2x80x9d is generally carried out as a separate and distinct process from the electroforming process. In this respect, the electroforming of the base copper foil generally takes place using a concentrated, hot copper sulfate/sulfuric acid electrolyte whereas the surface treatment usually requires a colder, more dilute electrolyte to produce fragile, powdery deposits on the surface of the copper foil.
Attempts have been made to surface treat electroformed copper as part of the electroforming process. See for example, U.S. Pat. No. 3,901,785 to Buzhinskaya et al. and U.S. Pat. No. 5,863,410 to Yates et al., both of which disclose an electroforming cell having a surface treatment anode following a main forming anode for surface treatment copper formed by the main forming anode. The surface treatment anode is immersed within the same electrolyte that is used to form the base copper foil. The cell shown in U.S. Pat. No. 3,901,785 to Buzhinskaya et al. attempts to control the concentration of the electrolyte solution in the vicinity of the surface treatment anode by isolating the surface treatment anode with a barrier element. The cell shown in U.S. Pat. No. 5,863,410 to Yates et al. attempts to control the concentration of the electrolyte in the vicinity of the treatment anode by introducing electrolytes near the surface treatment anode.
In both arrangements because the treatment anode is disposed adjacent the main forming anode in the electrolyte solution. The performance of the treatment anode is therefore affected by the composition (i.e., chemistry) of the electrolyte forced through the inner electrode gap. Further, gas generated during the electroforming process will bubble past the treatment anode further affecting its operation.
The present invention overcomes these problems and provides an electroforming cell having a main anode assembly for forming the base copper foil and a separate treatment anode for applying a surface treatment to the electroformed copper disposed in a separate and distinct electrolyte chamber separate from the main anode assembly, and a method of using the same.
In accordance with the present invention, there is provided an apparatus for producing metal foil, comprising a drum cathode having an outer plating surface. The drum cathode is partially immersed to a set level in an electrolyte bath and is rotatable in a fixed direction about a generally horizontal axis. A main anode assembly having a main anode is immersed in the electrolyte bath, the main anode having a semicylindrical curved anode surface facing the drum cathode. The main anode is dimensioned to be spaced from the plating surface of the drum cathode so as to define a generally uniform gap therebetween. An energy source is connected to the main anode for energizing the main anode. A chamber containing an electrolyte solution is disposed above the electrolyte bath and adjacent the cathode drum where the cathode drum exits the electrolyte bath. A treatment anode is immersed in the electrolyte solution in the chamber adjacent the drum cathode. An energy source is connected to the treatment anode for energizing the treatment anode.
In accordance with another aspect of the present invention, there is provided an electroforming process for producing copper foil having a surface treatment applied thereto, comprising the steps of rotating a cathode drum about a fixed axis past a primary anode that is dimensioned and positioned relative to the drum to create a uniform gap therebetween. Forcing an electrolyte solution through the gap while passing a direct, plating electric current through the first electrolyte solution from the anode to the cathode to electroform on the cathode drum a base copper foil. Moving the base copper foil on the drum past the primary anode and the electrolyte solution. Moving the base copper foil on the drum past an enclosure having a treatment anode that is dimensioned and positioned relative to the cathode drum to create a uniform space therebetween. Introducing an electrolyte solution into the enclosure and the space at a controlled rate while passing a direct, treating electric current through the electrolyte solution from the treatment anode to the cathode to deposit micronodules of copper.
It is an object of the present invention to provide an electroforming cell for forming a metallic foil wherein the cell includes means for applying a bonding treatment to a surface of the metallic foil.
It is another object of the present invention to provide an electroforming cell as described above wherein the means for applying a bonding treatment utilizes the electroforming solution used to form the metallic foil.
A still further object of the present invention is to provide an electroforming cell as described above having one or more treatment anodes that are isolated from the electrolyte bath and the anodes that form the base copper foil.
A still further object of the present invention is to provide an electroforming cell as described above wherein the flow of an electrolyte solution past the treatment anode(s) is controlled to be sufficiently slow as to deplete copper in the electrolyte solution to deposit micronodules of copper.
These and other objects will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims.